This invention is related to a control system for vibratory conveyors and, more particularly, to a control system for vibratory conveyors in which the force providing the vibratory motion to the trough conveying the material is controlled.
There are various systems for controlling the direction and/or speed of material being carried by a vibratory conveyor. The systems typically operate to change either the direction or the magnitude of a force applied to a trough mounted for vibratory motion, usually provided by a plurality of springs, on a support. For purposes of this description, change, alteration, varying or adjustment of a force means changing the magnitude of the force, the direction along which the force acts, or both.
An example of a system for changing the force direction utilizes a plurality of rotating shafts and associated eccentric weights to supply a cyclical force to the vibratory trough. This system uses a mechanism for adjusting the relative positioning of one or more of the rotating shafts carrying the eccentric weights which in turn varies the direction of the maximum throw to the trough of the conveyor. Such a eccentric weight system is described in detail in U.S. Pat. No. 5,064,053 in which a single rotating shaft bearing an eccentric weight is in a parallel relationship with and positioned between paired additional rotating shafts bearing eccentric weights. The centered single shaft rotates in one direction while the paired shafts rotate in the opposite direction but at the same number revolutions per minute. In any 360.degree. rotation of the shafts, all eccentric weights will be oriented so that the centrifugal forces, due to rotation of the eccentric weights, will be in the same direction, i.e., at the same angle with respect to the horizontal plane twice in the rotation. This provides a maximum resultant force, the aggregate centrifugal force, each time in that direction. Similarly, a minimum resultant force will be experienced twice in a 360.degree. rotation. By varying the orientation of the single shaft with respect to the paired shafts, the "phase angle" relationship between the single rotating shaft and the paired rotating shafts, can be changed, thus changing the direction or "angle of attack" of the maximum resultant force supplied to the trough. In the system of the '053 patent, all shafts are driven by a single motor and a belt and pulley (sheave) system. A mechanism is supplied that changes the orientation of the central shaft with respect to the paired shafts, thus changing the phase relationship. The adjustment of the central shaft can be accomplished even when the system is operating to vary the direction of the maximum resultant force supplied to the trough.
Still another example of a vibrating conveyor system having the capability of adjusting the resultant force is found in the description of U.S. Pat. No. 5,404,996. As described, this system has a pair of spaced and parallel rotating shafts each provided with crankshafts linked together by a plurality of arms pivotally connected to the underside of a trough. The shafts are rotatably driven by a single motor through a series of belts and pulleys. The trough is mounted on tuned springs attached to a base. The apparatus set forth in Patent '996 provided a significant advantage over other single eccentric crank shaft vibrating conveyors since the peak-to-peak displacement, i.e., maximum amplitude or displacement can be varied effectively between zero and a maximum. This is accomplished by a structure that permits the phase angle relationship between the rotating crankshafts to be mechanically adjusted thereby changing the amplitude of the displacement supplied to the trough.
None of the systems of the prior art, however, provide for the continuous and automatic adjustment of the phase angle relationship between shafts while in operation. Most require a mechanical structure consisting of pulleys, pivoting blocks mounting certain of the pulleys, and other mechanical devices to change the phase angle relationship between the "phase elements" associated with the rotating shafts, e.g., eccentric weights or crankshafts. Such structure occupies considerable space, often a significant operating detriment when the available manufacturing floor space for conveying equipment is limited. Moreover, continuous monitoring and adjustment of such systems during operation may be required to ensure that the proper angle phase relationship is maintained. It is therefore a paramount object of the present invention to provide for a system for adjusting the phase angle relationship between phase elements therein without the need for a complicated mechanical structure. It is still another important object of the present invention to provide for a system that continuously maintains a predetermined phase angle relationship during operation thereof. It is still a further object of the present invention to provide for a system for altering the phase relationships compatible with available limited manufacturing floor space.